A laboratory study of the effect of creep and fines migration on coal permeability during single-phase flow

Both fines migration and creep can damage coal permeability during coal seam gas production. This study investigates the individual and coupled effect of fines migration and creep on coal permeability. We perform three types of flow experiments on coal samples: (1) water flow with both fines migration and creep, (2) gas flow with creep and negligible fines migration, and (3) water flow with only fines migration. During the experiments involving creep, both radial and axial strains are measured. Analytical models for fines migration and creep are used to explain the permeability decrease during experiments. After stress was applied, the coal samples creep after elastic deformation. Fines migration or creep alone causes permeability reduction by about 25%, whereas their combined effect causes about a 60% reduction. Additional fines were generated due to stress loading causing additional pore blockage, which explains the greater permeability damage when both fines migration and creep are present. An expansive radial creep was observed, which is strongly correlated with permeability reduction. Existing creep model could not match the observed expansive radial creep.